1. Field of the Invention
The present invention relates to a deflection yoke for a color cathode-ray tube and a display using a deflection yoke.
2. Description of the Relative Art
FIG. 1 shows an example of a deflection yoke for use in a computer display.
A deflection yoke 11 comprises a cathode ray tube 1, horizontal deflection coil 2, a vertical deflection coil 3, a magnetic core 4, and other parts.
When a current is passed through the horizontal deflection coil 2, a horizontal deflection magnetic field is generated.
Three electron beams of a color cathode-ray tube 1 are scanned in the horizontal direction by the horizontal deflecting magnetic field.
When a current is passed through the vertical deflection coil 3, a vertical deflection magnetic field is generated and electron beams are scanned in the vertical direction.
A coil 5 is attached to a back cover 10 of the deflection yoke 11.
The back cover 10 is provided with a mechanism for attaching a member 6 having a magnetic substance.
Both the coil 5 and the member 6 are used to correct what is called misconvergence.
The coil 5 corrects the misconvergence by actively generating a magnetic field by the passage of a current from the outside to the coil 5.
On the other hand, the member 6 corrects the misconvergence by passively changing the horizontal deflection magnetic field.
The horizontal deflection magnetic field generated by the horizontal deflection coil 2 is changed by an influence of the magnetic substance attached to the member 6.
The degree of the change in the magnetic field varies according to the position of the magnetic substance of the member 6.
By the change in the horizontal deflection magnetic field, a slight change occurs in the tracks of the electron beams.
The convergence characteristic of the cathode-ray tube accordingly changes.
By adjusting the fitting position of the member 6, therefore, the convergence can be adjusted.
The back cover 10 is attached to the neck portion side of the deflection yoke 11, that is, to the electron gun side of the cathode-ray tube.
As shown in FIG. 2, conventionally, the members 6 each having a magnetic piece 7 are attached independently to the right and left sides of the back cover 10.
Whether or not the member 6 has to be used is determined at the time of manufacture of a computer display.
That is, when the member 6 is unnecessary for the correction of the misconvergence, the member 6 is not used.
On the other hand, when it is determined to be necessary, the member 6 is attached to either the right or left side of the back cover 10.
In the case of manufacturing computer displays of the same kind, a computer display having no member 6 and that having the member 6 mixedly exist.
Between them, due to the existence/absence of the member 6, there is a subtle difference in the convergence characteristic of the whole screen.
In recent years, as the resolution of the computer display becomes higher, the subtle variation in the convergence characteristic has been becoming unignorable.
In order to solve the problem, a method of disposing a member integrally having magnetic pieces on its both sides and simultaneously moving both of the right and left magnetic pieces, thereby correcting misconvergence, has been proposed.
In such a manner, the magnetic pieces are always used.
In an actual use, however, it is necessary to perform positioning, that is, to position both of the magnetic pieces to be symmetrical with respect to the electron gun as a center since this state corresponds to a standard state when the convergence is adjusted.
When the member is move d in the lateral direction from the standard state, the convergence changes according to the movement amount.
The visual positioning has, however, a drawback with respect to the efficiency of the work and reliability.
It is an object of the invention to provide a deflection yoke capable of simply and certainly positioning a member to which a pair of magnetic substances are attached as well as easily correcting misconvergence, and to provide a display having no variations in the convergence characteristic caused by the presence/absence of the member.
A deflection yoke according to the invention comprises a horizontal deflection coil, a vertical deflection coil, and a core.
A member for correcting misconvergence is attached to the neck part of the deflection yoke, that is, on the electron gun side.
The member has an opening, and a pair of magnetic pieces are attached to the member symmetrically with respect to the opening as a center.
The member is attached to the neck side of the deflection yoke so as to be mechanically movable in the horizontal deflection direction of an electron beam.
In such a state, the pair of magnetic pieces are arranged in the horizontal deflection direction.
The shape of each of the right and left ends of the member coincides with the outer shape of the rear part of the deflection yoke to which the member is attached.
According to the structure, by only moving the member so that the part coincides with the rear part of the deflection yoke, the member is set in the so-called standard state position.
To be specific, the pair of magnetic pieces of the member are set in the symmetrical positions with respect to the axis of the deflection yoke.
By moving the member in the lateral direction from the above state, an influence is exerted on a horizontal deflection magnetic field generated by the horizontal deflection coil.
After the deflection yoke is attached to the cathode-ray tube, the neck portion of the cathode-ray tube is inserted through the opening in the member.
When the member is moved in the lateral direction, the pair o magnetic pieces become asymmetrical and the horizontal deflection magnetic field of the neck portion changes.
Thus, by adjusting the movement amount in the lateral direction of the member, convergence can be adjusted.
Since the member is moved only in the lateral direction and always exists, the pair of magnetic pieces are always used.
In a display using the deflection yoke according to the invention, therefore, no subtle variation occurs in the convergence, the variation conventionally caused by the presence/absence of the magnetic pieces.
Thus, variations in the convergence characteristic are reduced in the manufacture of the same kind of displays.